Tomorrow I am going to be making a two layer Perfect All-American Chocolate Torte cake (love it!) for my nephew. I am afraid I will mess up the conversion from a single layer 9x2” pan (current recipe) to a double layer 9x13” pan. I am not going to split each layer. I will make the recipe two times and just use the cake layer as is. (I only have one Magic Line pan in this size and I love my straight sides!)

This is the process I was going to use:
-Double the original recipe since the Rose Factor chart starts with two layer cakes that are two inches high. The chart on p. 490 of TCB shows a 9x13 is Level 6. If I’m understanding correctly, I can use either 3.5 or 4 for my Rose Factor depending on if I want a taller cake. I will use 3.5 and multiply the doubled original recipe ingredient amounts by this number, except for the baking powder. For the baking powder, p.493 shows Level 6 with 1 1/3 tsp. baking powder, so I multiply 1 1/3 tsp. by 3.5 to get my baking powder amount for one pan of ingredients. I will bake the cake for 35-45 minutes, or until the cake gets to 190 degrees, at 350 degrees with cake strips around the pan. I will then repeat the whole thing to bake another layer.

Am I correct in my process? If it seems like I’m insecure about this because of all of my details, that is because I am! The last time I tried to convert a recipe, I messed up the baking powder and had to remake the cake. I don’t have time to start over on this one.

First, the PAACT is my fave chocolate cake so far, too!! I still have one or two I have to make, though.

Remember that the Rose factor only really works for the specified cakes—any other cake is experimental.

Basically, baking powder works like this: It weakens the structure. The structure is your cake having to hold itself up across the diameter of the pan. Too much structure, and you get a dome. Too little, and it’s sunken. So a pan with less diameter will use a bit more BP that a pan with greater diameter—you want a stronger structure for a wider pan, and baking powder weakens the structure.

With a 9x13, you have two different spans.

My guess is you will double the recipe for each 9x13 (as you say), but you’ll want to not quite double the BP is my guess. I’ve heard 9x13s can be iffy—and I’ve never worked with the Rose factor, but I wasn’t sure if any of that info would be helpful at all in a sort of general way!

Thanks, Anne, for your help! I ended up figuring out the exact volume ratio, which was 1.839… and using that amount for each layer of cake. The layers were a perfect height, and I ended up with way too much cake. Better to have more than not enough! I used a little less than double the baking powder, but the cake dipped in the center while it was cooling. I guess that means I should have used more baking powder. It still tasted delicious!

Actually, if it dipped, it could be that you needed LESS baking powder. Remember, baking powder WEAKENS the structure, and your center dipped, so the center wasn’t strong enough—it was too weak to hold itself up.

Of course, it could dip for other reasons, too—if, by chance, you were using UNBLEACHED all purpose flour. If so, you need even less BP.

However, I’ve had cakes dip on me, and I never considered it a problem—it was simply a “more frosting” opportunity!!! I think those dipped centers are so delicious, dense and moist, too. Even though I don’t hope for them, I never mind the occasional occurrence! And on a chocolate cake, it’s just more fudgy, which is never bad!

Sometimes, people use those sort of “cores” in 9x13s also. It’s this sort of ring you put in the batter, and, because it’s metal, it conducts heat to the center, so it can cook more evenly there. It’s kind of like the theory of a bundt pan, but applied to a layer. I’ve never used one, myself, so I can’t speak from experience, only theory.

I don’t know why the bp confuses me! I didn’t bother leveling it out. I just used extra filling since the slices were squares and not pie wedges so the layering difference wasn’t as obvious. I use bleached flour. I try to use only what Rose recommends if possible. Less chance of messing it up! Also, I never thought to use my core for a rectangular cake. I’ve only used it with larger rounds. Good idea to try.

By the way, the PAACT is my favorite chocolate cake also of the ones I’ve made. So good!!! I made a Cookies and Cream filling and White Chocolate Mousseline for the frosting. I hate to say it, but I think I like my frosting a little sweeter. I’ve made the mousseline three times so I know I’m not messing up the recipe. It turns out the way it is supposed to, but I like the frosting, not love it. I haven’t added a flavoring besides vanilla though since I’m always making the cakes for the family. I’m not really concerned about giving my kids the little bit of alcohol in the frosting, but I’m not so sure everyone feels the same way. How do you feel about the other frosting recipes?

The mousseline is a tad sweeter than the other buttercreams (neoclassic and silk meringue). You could try the white chocolate version of mousseline for a slight increase in sweetness along with an improved richness and mouthfeel. I don?t much care for white chocolate but I do like white chocolate mousseline better than straight vanilla. The fruit curd and puree versions are wonderful, and the curd or puree can be made a little sweeter if you want a sweet frosting.